1. Field of the Invention
The present invention relates to an alarm apparatus. In particular, the present invention relates to an alarm apparatus which, in use, is associated with an object, such as a machine, plant, tool, vehicle or the like, or a person, and is activated in the event that said object or person comes into contact with, or has a dangerous voltage potential induced from an electrical supply network and hence, becomes energised or live with voltages typical of such electrical supply networks.
2. The Prior Art
Persons working in the vicinity of power cables, for example, pylons and underground cables, run the risk of being electrocuted, since the vehicle in which they are located, or the machines or tools with which they are working, which are capable of conducting electricity, may become energised by the discharge of electricity from said power cables. Consequently, any resultant casual contact with such energised vehicles, tools or machines may result in injury or even death.
Accidents of this type sometimes occur in the tree maintenance industry, particularly those persons involved in live power-line tree clearing, i.e. the removal or pruning of trees in the vicinity of power cables which are energised using access platforms.
In order to reduce such associated injuries and fatalities, attempts have been made to insulate said objects or parts of said objects which are likely to be energised by said power cables, for example, mobile access platforms associated with a vehicle utilised for live-line clearing. However, due to the nature of the work, the insulation may become damaged, breached or by-passed thereby exposing parts of the vehicle or machine which are capable of becoming energised to, or close to, ground level.
Therefore, although the insulation described above may reduce the occurrence of such electrocution, the risk of such associated injuries and fatalities are still unacceptably high and represent a hazard to anybody who could come into casual contact with a passively energised object.
With a view to overcoming the above problem, there has been provided alarm apparatus which are adapted to alert any person working in close proximity to power cables or other electricity carrying means that the vehicle in which they are located, or the tool or machine with which they have come into contact, has become energised to a dangerous voltage, i.e. such alarm apparatus warns such persons of the unseen danger of energisation, thereby enabling such person to take all the necessary steps in order to avoid contact with such energised object and hence, observe proximity zone guidelines to safely resolve the hazard by not touching the machinery and not allowing anybody else to do so. An example of an alarm apparatus of this type is disclosed by European Patent Application No. 87304611.4 (Flowmole Corporation).
Generally, and with reference to FIG. 1, known alarm apparatus of this type comprise first and second circuits which are isolated from one another, as well as being antagonistic to one another.
The first circuit comprises a prod 30, a switch means 40 and a conducting wire 50, connected in series. The second circuit comprises a power supply 20, the switch means 40 and alarm means 10, connected in series.
As shown in FIG. 2 a suitable switch means 40 for such an alarm apparatus, developed by us, comprises a ceramic U-shaped clamp 41 which, in use, is attached to the object. Said switch means 40 comprises a bi-metallic strip 42 which acts as a bridge between the conducting wire 50 on one side of the switch means 40 and the prod 30 connected to the other side of the switch means 40. Said switch means 40 also comprises a spring-loaded switch 44 movably located therein.
The bimetallic strip 42 of the switch means 40 is fastened at end 45 by fixing means 43 and is in contact with conducting wire 50 which is attached to a part of the object "X" which is capable of becoming energised. The opposite end 46 of the bi-metallic strip 42 is in contact with the prod 30.
Whilst such known alarm apparatus is inactive, i.e. the object to which it is attached or associated with has not become energised, the first circuit is complete and the end 46 of the bi-metallic strip depresses the spring-loaded switch 44. Consequently, the second circuit is incomplete or broken, i.e. the power source 20 is not connected to the alarm means 10.
On energisation of the object, the resultant flow of electricity to earth causes side 46 of the bi-metallic strip 42 to lift, thereby releasing said spring loaded switch 44. As a result thereof, the second circuit is now complete and the alarm means 10 are activated, that is, as a result of the power source 20 and the alarm means 10 being connected.
When a vehicle (not illustrated), equipped with such an alarm apparatus, comes to a standstill in the vicinity of power cables, the prod 30 is inserted into the ground thereby completing the first circuit.
In the event that the vehicle becomes energised, an electric discharge will surge through the first circuit, i.e. to earth. Depending on the design parameters of the bi-metallic strip 42, if the voltage driving the electric discharge is of sufficient strength, end 46 of the bi-metallic strip 42 will lift or completely burn out, thereby resulting in the release of the spring-loaded switch 44. The subsequent release of the spring-loaded switch 44 results in the completion of the second circuit and hence, the activation of the alarm means 10. Thus in the event of energisation, a person in the vicinity of the vehicle can take all the necessary steps in order to avoid contact with such energised object and hence, observe proximity zone guidelines to safely resolve the hazard.
The problem associated with known alarm apparatus of this type is that in order to work, they are required, in use, to be earthed. Failure to do so will result in the alarm apparatus not being activated such that a person utilising such an alarm apparatus will not be made aware of any pending danger of coming into contact with an object which may have become energised.